Nemexnos, Abyssal Champion

As long as Nemexnos's power is more than 5, it has Firststrike.
Oath of Vengeance- Whenever you take damage, put a +1/+1 counter on Nemexnos, than have it fight target creature.
Oath of Conquest- Whenever a source you control kills a creature you don't control, put a +1/+1 counter on Nemexnos and create a 2/1 red and black demon token with deathtouch.